Can't send

[MTRNord]

When I try to use

 session.sendMessage({
  channel: '#github',
  text: 'omg'
});

It crashes with the following error. Why does that happen?

M:\github\nordlab-hackerspace-door\node_modules\slackr-bot\lib\session.js:249
    this.ws.send(str);
           ^

TypeError: Cannot read property 'send' of undefined
    at Object.Session.send (M:\github\nordlab-hackerspace-door\node_modules\slac
kr-bot\lib\session.js:249:12)
    at Object.Session.sendMessage (M:\github\nordlab-hackerspace-door\node_modul
es\slackr-bot\lib\session.js:239:12)
    at Object.<anonymous> (M:\github\nordlab-hackerspace-door\handlers\slack.js:
53:9)
    at Module._compile (module.js:413:34)
    at Object.Module._extensions..js (module.js:422:10)
    at Module.load (module.js:357:32)
    at Function.Module._load (module.js:314:12)
    at Module.require (module.js:367:17)
    at require (internal/module.js:16:19)
    at Object.<anonymous> (M:\github\nordlab-hackerspace-door\main.js:20:13)

npm ERR! Windows_NT 6.1.7601
npm ERR! argv "C:\\Program Files\\nodejs\\node.exe" "C:\\Program Files\\nodejs\\
node_modules\\npm\\bin\\npm-cli.js" "start"
npm ERR! node v5.8.0
npm ERR! npm  v3.7.3
npm ERR! code ELIFECYCLE```